fakeservicemanager: Add a clear() method am: 8cc776ae71 am: d90caf0b00 am: 6b3460db15

Original change: https://android-review.googlesource.com/c/platform/frameworks/native/+/2308645

Change-Id: I99f70c0b5e6baf8edd1780df21e2a2817b3f1f63
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>